The present invention is directed, in general, to micro-electromechanical system (MEMS) devices and, more specifically, to a driver and method of operating the MEMS device.
Electrostatically actuated micro-electromechanical system (MEMS) devices have been proposed for a variety of applications. One promising use for MEMS devices is in optical switching and steering devices. In such devices, movable micro-machined mirrors are used as a switching element to direct an input optical signal to a desired output. The movement of the micro-machined mirrors is accomplished by electrostatic actuation.
In a typical MEMS device, an individual mirror is affixed to a movable support structure (i.e., a gimbal) via torsional elements such as springs. The gimbal may be coupled to a frame, also via torsional elements. Typically, two torsional elements positioned on opposing sides of the mirror, couple the mirror to the gimbal, and define an axis for mirror rotation. Similarly, two torsional elements positioned on opposing sides of the gimbal couple the gimbal to the frame, and define an axis for gimbal rotation.
In a typical situation, electrodes are positioned under the mirror and gimbal. The electrodes are configured to rotate the mirror or gimbal in either direction about its axis. The mirror or gimbal rotates under the electrostatic force between the mirror and gimbal, and is balanced in equilibrium by the restoring force of the torsional elements. The degree of rotation depends upon the amount of voltage applied to the electrodes. Traditionally, a degree of rotation up to about 9 degrees is achievable. With the above-mentioned designs, a voltage of greater than about 150 volts may be required.
Currently, there is a desire to use lower actuation voltages to rotate the mirror and gimbal structures. The lower actuation voltages open up options for conventional electronic drivers instead of using a custom high-voltage process. One of the disadvantages with the traditional switching element disclosed above is that it can not adequately operate at the lower voltages. As previously mentioned, the torsional elements are designed for a maximum actuation voltage of greater than about 150 volts and a gimbal resonant frequency of about 300 Hz.
It has been found that by reducing the stiffness of the torsional elements, the MEMS devices may be rotated using substantially reduced voltages, either in the mirror direction or the gimbal direction. However, reducing the stiffness of the torsional elements in order to reduce the voltage to about 75 volts, in accordance with the capability of the electronic drivers, is not an attractive option because the resonant frequency will drop to about 150 Hz, substantially reducing the switching speed. In addition, the torsional elements may be excessively long and weak, leading to potential failure during fabrication or significant vertical (downward) sag during operation.
Accordingly, what is needed in the art is a MEMS device, and an associated driver that overcomes the deficiencies in the prior art.
To address the above-discussed deficiencies of the prior art, the present invention provides a driver for use with a micro-electromechanical system (MEMS) device, method of operation thereof, and a MEMS device employing the driver and method. In one embodiment, the driver includes an actuation subsystem that provides an actuation voltage to alter an angle of an optical element of the MEMS device. The driver also includes a bias subsystem, coupled to the actuation subsystem, that applies a bias voltage between the optical element and the actuation subsystem, thereby reducing the actuation voltage.
Thus, in one aspect, the present invention is capable of operating at a substantially lower actuation voltage than the prior art devices. Moreover, the lower voltage operation further allows An the MEMS device to be operated with reduced power consumption and increased reliability. Likewise, the present invention may accomplish the substantially lower actuation voltage without a substantial reduction in rotation angles and rotation speed.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.